1. Field of the Invention
The present invention relates to a liquid crystal display apparatus which offers high display quality.
2. Description of the Related Art
The conventional liquid crystal display apparatus will be described below.
A CRT (Cathode Ray Tube) type has been heretofore on the main stream of a display apparatus. Today, however, this stream is oriented to an active matrix type LCD (Liquid Crystal Display) apparatus. This LCD is a display apparatus that utilizes light transmittance involved in liquid crystal materials without providing no light-emitting capability. It displays an image by passing through or cutting off light emitted from a backlight unit located on the rear surface of the liquid crystal material
Heretofore, a fluorescent tube has been mainly used as the backlight unit of the LCD apparatus. Today, it is reported that an LED (Light-emitting Diode) is used as the backlight unit of the LCD for the purpose of improving color representability of a displayed image. For example, this technology is described in SID '02 Digest P. 1154.
The LED backlight unit described in SID '02 Digest P. 1154 needs to provide a proper feedback circuit for displaying the same color for a considerable length of time, because a red (referred simply to as “R”) LED has a different temperature characteristic from a green (referred simply to as “G”) LED or a blue (referred simply to as “B”) LED.
On the other hand, it is reported in SID '03 Digest P. 1254 that a feedback circuit is composed of backlight sensors of three colors so that color adjustment may be executed by adjusting a luminous period of each color.
A notarized personal computer display or a desktop personal computer monitor has been heretofore on the main stream of the products to which the LCD apparatus is applied. Today, the use of the LCD apparatus is oriented to a TV receiver. An image display apparatus used in the TV receiver is required to represent an object with fidelity and beautifully as viewed by a watcher. As one example, the CRT realizes a display in a more dynamic range than a contrast ratio appearing in an overall image display by using the white-peak display characteristic.
For realizing a more visibly beautiful image on a display, in some cases, the LCD apparatus is arranged to expand a dynamic range by dynamically adjusting a contrast and a backlight luminance according to a video signal being inputted thereto as described in Japanese Patent No. 3215400 or to enhance visibility by changing a display luminance according to a measured ambient light quantity as described in JP-A-6-214508.
The LCD display is changed from black to white or white to black in response to a voltage change. In the conventional LCD apparatus, the response time of the LCD display change from black to white or white to black is as slow as 10 to 30 milliseconds. Further, the response time from white to halftone or from black to halftone is as slow as 20 to 50 milliseconds and thus is slower than the former response time. It means that an after-image phenomenon is brought about on a TV image containing lots of halftones and moving objects.
The foregoing conventional LCD apparatuses currently have a “holding type” display system that continuously outputs the same image during a period of one frame, that is, one period of a video signal.
In these “holding type” system LCD apparatus, when a moving image such as a TV image is displayed, the image that has to be moving in sequence is displayed at the same location during a period of one frame. That is, though an image at a proper location is displayed at an instant point of one frame, an image at an improper location is displayed at another instant point of one frame. That is, the displayed image is actually at another location. A watcher watches the averaged one of these images, so that the watcher may feel the image vague. This phenomenon will be discussed in detail in the technical report of the literary society of Electric, Information and Communications, EID99-10, pp. 55-60 (1999-06) or reported in SID'01 Digest, p. 986 (2001).
With respect to the response speed of the foregoing problems, there has been proposed a technology of comparing a video signal from a video signal source of a current frame with a video signal of a one previous frame, if a change between these video signals is detected, converting the video signal so that the change may be made greater and changing the display of concerned pixels according to the values corresponding with the original video signal until the next frame. This technology is discussed in SID '92 Digest, p. 601 (1992), H. Okumura et al, for example. This technology allows the speed of the halftone response to be equal to the speed of the response from white or black or vice versa, thereby being able to improve an after image when displaying a moving image.
Further, for overcoming a blur of a moving image caused by the light emission of the holding type LCD apparatus, for example, the technology of eliminating a blur portion caused by the averaging is discussed in IDRC '97 Digest, p. 203 (1997), Sueoka et al, for example. Concretely, this technology takes the steps of making the liquid crystal responsive by scanning the overall liquid crystal panel and causing the lighting device to be active thereafter.
Though the foregoing technologies have been proposed, however, for enhancing the image quality of a TV receiver provided with the LCD apparatus, that is, a liquid crystal TV, it is necessary to solve the problems involved in the background of the invention. That is, the foregoing background technologies do not meet the three respects of (1) a wide dynamic range for a well-modulated image, (2) so wide color gamut as outputting vivid colors and (3) a vivid image with no blur of a moving image, for the purpose of displaying a high-quality and visibly beautiful image on the liquid crystal TV.
It is an object of the present invention to solve the foregoing problems, that is, provide an LCD apparatus which offers a wide dynamic range and wide color gamut and no blur of a moving image when displaying an image.